Groovy Closure Support for Java

Groovy Closure Support for Java enables using closure delegation shortcuts on coerced closures.

Support setting delegate of closures coerced to single abstract method interfaces as well as for closures coerced to single abstract method abstract classes.

Imagine you have simple builder class which you want to use in Groovy-builder style to create nested structures.

class PointBuilder {
    PointBuilder x(int x);
    PointBuilder y(int y);
}

import java.util.function.Consumer;

class PointSource {
    Point add(Consumer<PointBuilder> pointConsumer) {
        PointBuilder point = new MyPointBuilder();
        // sets the delegate if Groovy Closure wrapper
        GroovyClosure.setDelegate(pointConsumer, point);
        pointConsumer.accept(point);
    }
}

In Java code you can get as close as to use for example java.util.function.Consumer to which you pass the builder for the inner element and than call the methods on the builder object.

class JavaUsage {
    void addPointToSource(PointSource source) {
        source.add(point -> {
            point.x(0);
            point.y(100);
        });
        source.add(point -> point.x(2).y(3));
    }
}

On the other hand when Groovy is on the classpath and instead of Java object a Groovy closure is passed to the method then GroovyClosure.setDelegate(pointConsumer, point) will recognize it and sets the closure delegate to object passed as second argument and also sets the resolve strategy to DELEGATE_FIRST so you don't have to prefix the method calls with the builder object any longer.

class GroovyUsage {
    void addPointToSource(PointSource source) {
        source.add {
            x 0
            y 100
        }
        source.add { x 2 y 3 }
    }
}

Another approach is to create a Groovy extension which will itself accepts Closure and use ConsumerWithDelegate, FunctionWithDelegate or PredicateWithDelegate to wrap closure as Consumer, Function or Predicate. This approach is preferred as it gives more options for static compilation hints.

class PointExtensions {

    public static Point add(
        PointSource self,
        @DelegatesTo(value = PointBuilder.class, strategy = Closure.DELEGATE_FIRST)
        @ClosureParams(value = SimpleType.class, options = "com.example.PointBuilder")
        Closure builder
    ) {
        return self.add(ConsumerWithDelegate.create(builder));
    }

}

Setup

The binaries are hosted on Maven Central

Gradle

repositories {
    mavenCentral()
}

dependencies {
    implementation 'space.jasan:groovy-closure-support:1.0.0'
}

Maven

<dependency>
  <groupId>space.jasan</groupId>
  <artifactId>groovy-closure-support</artifactId>
  <version>1.0.0</version>
  <type>pom</type>
</dependency>

Version Compatibility

This utility is tested against following JVMs

• OracleJDK 8

and only Groovy 4.x is supported.

Use the previous version space.jasan:groovy-closure-support:0.6.2 for the Groovy 2.x and 3.x support.